<template>
  <div class="pagination">
    <button :disabled="pageNo == 1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button 
    v-if="startNumAndEndNum.start > 1" 
     @click="$emit('getPageNo', 1)"
    :class="{ active: pageNo == 1 }"
    >
    1
    </button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

<!-- 中间部分 -->
    <button 
    v-for="(page, index) in startNumAndEndNum.end" :key="index" 
    v-if="page >= startNumAndEndNum.start" 
    @click="$emit('getPageNo',page)" 
    :class="{ active: pageNo == page }"
    >
    {{ page }}
    </button>
    
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button 
    v-if="startNumAndEndNum.end < totalPage" 
    @click="$emit('getPageNo', totalPage)" 
    :class="{ active: pageNo == totalPage }"
    >
    {{ totalPage }}
    </button>
    <button 
    :disabled="pageNo == totalPage" 
    @click="$emit('getPageNo', pageNo + 1)"  
    >
    下一页
    </button>
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props:['pageNo','pageSize','total','continues'],
    computed:{
      // 总共多少页
      totalPage(){
        // 向上取整
        return Math.ceil(this.total/this.pageSize)
      },
      //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
      startNumAndEndNum() {
        const { continues, pageNo, totalPage } = this;
        //先定义两个变量存储起始数字与结束数字
        let start = 0,
          end = 0;
        //连续页码数字5【就是至少五页】，如果出现不正常的现象【就是不够五页】
        //不正常现象【总页数没有连续页码多】
        if (continues > totalPage) {
          start = 1;
          end = totalPage;
        } else {
          //正常现象【连续页码5，但是你的总页数一定是大于5的】
          //起始数字
          start = pageNo - parseInt(continues / 2);
          //结束数字
          end = pageNo + parseInt(continues / 2);
          //把出现不正常的现象【start数字出现0|负数】纠正
          if (start < 1) {
            start = 1;
            end = continues;
          }
          //把出现不正常的现象[end数字大于总页码]纠正
          if (end > totalPage) {
            end = totalPage;
            start = totalPage - continues + 1;
          }
        }
        return { start, end };
      },
    }
  }
</script>


<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active{
  background: skyblue;
}
</style>